U.S. patent number 5,376,869 [Application Number 08/016,551] was granted by the patent office on 1994-12-27 for electric vehicle drive train with rollback detection and compensation.
This patent grant is currently assigned to General Electric Company. Invention is credited to Charles E. Konrad.
United States Patent |
5,376,869 |
Konrad |
December 27, 1994 |
**Please see images for:
( Certificate of Correction ) ** |
Electric vehicle drive train with rollback detection and
compensation
Abstract
An electric vehicle drive train includes a controller for
detecting and compensating for vehicle rollback, as when the
vehicle is started upward on an incline. The vehicle includes an
electric motor rotatable in opposite directions corresponding to
opposite directions of vehicle movement. A gear selector permits
the driver to select an intended or desired direction of vehicle
movement. If a speed and rotational sensor associated with the
motor indicates vehicle movement opposite to the intended direction
of vehicle movement, the motor is driven to a torque output
magnitude as a nonconstant function of the rollback speed to
counteract the vehicle rollback. The torque function may be either
a linear function of speed or a function of the speed squared.
Inventors: |
Konrad; Charles E. (Roanoke,
VA) |
Assignee: |
General Electric Company
(Schenectady, NY)
|
Family
ID: |
21777708 |
Appl.
No.: |
08/016,551 |
Filed: |
February 11, 1993 |
Current U.S.
Class: |
318/587; 701/22;
318/139; 180/282; 318/373 |
Current CPC
Class: |
B60L
50/66 (20190201); B60L 50/16 (20190201); B60L
15/2009 (20130101); B60L 15/2018 (20130101); Y02T
10/7275 (20130101); B60W 30/18118 (20130101); Y02T
10/7072 (20130101); Y02T 10/645 (20130101); B60L
2250/26 (20130101); Y02T 10/7005 (20130101); B60L
2240/423 (20130101); B60L 2240/12 (20130101); B60L
2240/486 (20130101); Y02T 10/64 (20130101); Y02T
10/7077 (20130101); Y02T 10/72 (20130101); B60L
2240/421 (20130101); Y02T 10/70 (20130101); Y02T
10/705 (20130101) |
Current International
Class: |
B60L
15/20 (20060101); H02P 003/10 (); H02H
003/17 () |
Field of
Search: |
;318/560-646,139,370-376
;364/424-426 ;180/282,65A ;188/2D ;361/31,58,93,87
;192/4A,3TR,9 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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0374960 |
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Jun 1990 |
|
EP |
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0585122A2 |
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Mar 1994 |
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EP |
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2660258 |
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Oct 1991 |
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FR |
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2411550 |
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Sep 1975 |
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DE |
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WO84/02813 |
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Jul 1984 |
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WO |
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WO93/04888 |
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Mar 1993 |
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WO |
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Primary Examiner: Ip; Paul
Attorney, Agent or Firm: Bell, Seltzer, Park &
Gibson
Government Interests
GOVERNMENT RIGHTS
The Government of the United States of America has rights in this
invention pursuant to Contract No. DE-AC07-90ID13019 (Subcontract
No. 47-2-111883) awarded by the U.S. Department of Energy.
Claims
That which is claimed is:
1. A drive train for an electric vehicle, said drive train
comprising:
an electric motor for driving one or more wheels of the vehicle and
being rotatable in opposite directions corresponding to respective
opposite directions of actual vehicle movement, said electric motor
having a controllable torque output magnitude;
sensing means associated with said electric motor for sensing
rotational speed and direction thereof;
selector means for permitting driver selection of a direction of
intended vehicle movement; and
rollback detection and compensation means connected to said
electric motor, and responsive to said sensing means and said
selector means, for determining vehicle rollback defined by a
sensed direction of actual vehicle movement opposite to a selected
direction of intended vehicle movement and for controlling the
output torque magnitude of said electric motor responsive to sensed
rotational speed of said electric motor and as a predetermined
function thereof to counteract the vehicle rollback.
2. A drive train according to claim 1 wherein said rollback
detection and compensation means includes means for controlling the
output torque magnitude of said electric motor as a nonconstant
function of rotational speed of said electric motor during vehicle
rollback.
3. A drive train according to claim 1 wherein said rollback
detection and compensation means includes means for controlling the
output torque magnitude of said electric motor as a linear function
of rotational speed of said electric motor during vehicle
rollback.
4. A drive train according to claim 1 wherein said rollback
detection and compensation means includes means for controlling the
output torque magnitude of said electric motor as a function of
rotational speed squared of said electric motor during vehicle
rollback.
5. A drive train according to claim 1 wherein said rollback
detection and compensation means includes means for controlling the
output torque magnitude of said electric motor at a predetermined
constant value responsive to a rotational speed of said electric
motor being above a predetermined value.
6. A drive train according to claim 1 further comprising a traction
battery connected to said electric motor.
7. A drive train for an electric vehicle, said drive train
comprising:
a traction battery;
an electric motor connected to said traction battery for driving
one or more wheels of the vehicle, said electric motor being
rotatable in opposite directions corresponding to respective
opposite directions of actual vehicle movement, said electric motor
having a controllable torque output magnitude;
sensing means associated with said electric motor for sensing
rotational speed and direction thereof;
selector means for permitting driver selection of a direction of
intended vehicle movement; and
rollback detection and compensation means connected to said
electric motor, and responsive to said sensing means and said
selector means, for determining vehicle rollback defined by a
sensed direction of actual vehicle movement opposite to a selected
direction of intended vehicle movement and for controlling the
output torque magnitude of said electric motor responsive to sensed
rotational speed of said electric motor and as a nonconstant
function thereof to counteract the vehicle rollback.
8. A drive train according to claim 7 wherein said rollback
detection and compensation means includes means for controlling the
output torque magnitude of said electric motor as a linear function
of rotational speed of said electric motor during vehicle
rollback.
9. A drive train according to claim 8 herein said rollback
detection and compensation means includes means for controlling the
output torque magnitude of said electric motor as a function of
rotational speed squared of said electric motor during vehicle
rollback.
10. A drive train according to claim 9 wherein said rollback
detection and compensation means includes means for controlling the
output torque magnitude of said electric motor at a predetermined
constant value responsive to a rotational speed of said electric
motor being above a predetermined value.
11. A drive train for an electric vehicle, said drive train
comprising:
an electric motor for driving one or more of wheels of the vehicle
and being rotatable in opposite rotational directions corresponding
to opposite directions of vehicle movement, said electric motor
having a controllable torque magnitude;
sensing means associated with said electric motor for sensing
rotational speed and direction thereof;
selector means for permitting driver selection of a direction of
intended vehicle movement;
driver input means for permitting driver selection of vehicle
braking or vehicle acceleration; and
control means connected to said electric motor for controlling the
output torque magnitude and rotational direction thereof in
response to said driver input means, said control means further
comprising rollback detection and compensation means responsive to
said sensing means and said selector means for determining vehicle
rollback defined by a sensed direction of actual vehicle movement
opposite to a selected direction of intended vehicle movement and
for controlling the output torque magnitude of said electric motor
responsive to sensed rotational speed of said electric motor and as
a nonconstant function thereof to thereby counteract the vehicle
rollback even in an absence of driver selection of one of vehicle
braking and vehicle acceleration.
12. A drive train according to claim 11 wherein said rollback
detection and compensation means comprises means for generating a
first torque request value as a nonconstant function of rotational
speed of said electric motor during vehicle rollback, wherein said
control means comprises means for generating a second torque
request value responsive to said driver input means during vehicle
rollback, and wherein said control means further comprises means
for adding the first and second torque request values for
controlling the output torque magnitude of said electric motor.
13. A drive train according to claim 11 wherein said control means
includes means for controlling the output torque magnitude of said
electric motor as a linear function of rotational speed of said
electric motor during vehicle rollback.
14. A drive train according to claim 11 wherein said control means
includes means for controlling the output torque magnitude of said
electric motor as a function of rotational speed squared of said
electric motor during vehicle rollback.
15. A drive train according to claim 11 wherein said control means
includes means for controlling the output torque magnitude of said
electric motor at a predetermined constant value responsive to a
rotational speed of said electric motor being above a predetermined
value.
16. A drive train according to claim 11 further comprising a
traction battery connected to said electric motor.
17. An electric vehicle comprising:
a frame;
one or more vehicle wheels rotatably mounted on said frame;
a traction battery carried by said frame;
an electric motor connected to said traction battery for driving
one or more wheels of the vehicle, said electric motor being
rotatable in opposite directions corresponding to respective
opposite directions of actual vehicle movement, said electric motor
having a controllable torque output magnitude;
sensing means associated with said electric motor for sensing
rotational speed and direction thereof;
selector means for permitting driver selection of a direction of
intended vehicle movement;
driver input means for permitting driver selection of vehicle
braking or vehicle acceleration; and
control means connected to said electric motor for controlling the
output torque magnitude and rotational direction thereof in
response to said driver input means, said control means further
comprising rollback detection and compensation means responsive to
said sensing means and said selector means for determining vehicle
rollback defined by a sensed direction of actual vehicle movement
opposite to a selected direction of intended vehicle movement and
for controlling the output torque magnitude of said electric motor
responsive to sensed rotational speed of said electric motor and as
a nonconstant function thereof to thereby counteract the vehicle
rollback even in an absence of driver selection of one of vehicle
braking and vehicle acceleration.
18. A drive train according to claim 17 wherein said rollback
detection and compensation means comprises means for generating a
first torque request value as a function of rotational speed of
said electric motor during vehicle rollback, wherein said control
means comprises means for generating a second torque request value
responsive to said driver input means during vehicle rollback, and
wherein said control means further comprises means for adding the
first and second torque request values for controlling the output
torque magnitude of said electric motor.
19. A drive train according to claim 17 wherein said control means
includes means for controlling the output torque magnitude of said
electric motor as a linear function of rotational speed of said
electric motor during vehicle rollback.
20. A drive train according to claim 17 wherein said control means
includes means for controlling the output torque magnitude of said
electric motor as a function of rotational speed squared of said
electric motor during vehicle rollback.
21. A drive train according to claim 17 wherein said control means
includes means for controlling the output torque magnitude of said
electric motor at a predetermined constant value responsive to a
rotational speed of said electric motor being above a predetermined
value.
22. A method for operating an electric vehicle including an
electric motor for driving one or more wheels of the vehicle and
being rotatable in opposite directions corresponding to respective
opposite directions of actual vehicle movement, and a selector for
permitting driver selection of a direction of intended vehicle
movement, said method comprising the steps of:
sensing a rotational direction of the electric motor corresponding
to a respective direction of actual vehicle moment;
determining vehicle rollback defined by the sensed direction of
actual vehicle movement being opposite the intended direction of
vehicle movement;
sensing a rotational speed of the electric motor corresponding to a
respective speed of actual vehicle movement; and
controlling an output torque magnitude of the electric motor
responsive to the sensed rotational speed of the electric motor and
as a predetermined function thereof to counteract the vehicle
rollback.
23. A method according to claim 22 wherein the step of controlling
the electric motor to counteract the vehicle rollback comprises
controlling the electric motor at an output torque magnitude as a
nonconstant function of sensed rotational speed of the electric
motor.
24. A method according to claim 23 wherein the step of controlling
the electric motor at an output torque magnitude comprises
controlling the electric motor at an output torque as a linear
function of sensed rotational speed of the electric motor.
25. A method according to claim 23 wherein the step of controlling
the electric motor at an output torque magnitude comprises
controlling the electric motor at an output torque as a function of
sensed rotational speed squared of the electric motor.
26. A method according to claim 22 wherein the step of controlling
the electric motor to counteract the vehicle rollback comprises
controlling the electric motor even in an absence of driver
selection of one of vehicle braking and vehicle acceleration.
27. A method according to claim 26 further comprising the steps of
generating a first torque request value as a nonconstant function
of rotational speed of said electric motor during vehicle rollback,
and generating a second torque request value responsive to driver
input for either of braking or acceleration of the vehicle; and
wherein the step of operating the electric motor comprises adding
the first and second torque request values for operating the
electric motor.
Description
FIELD OF THE INVENTION
The present invention relates to the field of electric vehicles,
and more particularly, to a drive train for an electric vehicle
including control of electric motor torque output.
BACKGROUND OF THE INVENTION
Electric vehicles are receiving considerable attention as a
substitute for present gasoline-fueled vehicles. This interest is
based primarily on zero atmospheric emissions obtainable from an
all-electric vehicle. Several states are considering stricter
emissions regulations for vehicles, and California has adopted
regulations that will require zero emissions for a percentage of
vehicles in certain urban areas. Electric vehicles also offer other
advantages including reducing dependency on imported oil, since
utilities in the United States generate a large portion of their
energy demands using coal, gas, nuclear, and hydroelectric
sources.
Even hybrid electric vehicles, such as those incorporating a small
gasoline engine running at a constant speed to recharge an electric
traction battery, offer anticipated lower emissions. See, for
example, U.S. Pat. No. 4,351,405 to Fields et al. which discloses a
hybrid vehicle including a gasoline engine for driving the front
wheels during high speed and long distance driving, while the rear
wheels are connected to electric motors for low speed and stop and
go driving.
To obtain widespread acceptance as a suitable substitute for
conventional gasoline-fueled vehicles, an electric vehicle should
desirably mimic the operation of such a conventional gasoline
vehicle, especially the drive train including a conventional
automatic transmission. Functions such as braking and acceleration
are readily controlled in an electric vehicle through a
conventional brake pedal and accelerator pedal. The selection of
drive, reverse, park, and neutral positions are also imitated on an
electric vehicle. However, in a conventional gasoline vehicle, the
engine always rotates in a same direction and the vehicle includes
a clutch or fluid coupling to transmit torque to the vehicle
wheels. In other words, a conventional automatic transmission will
tend to start the vehicle moving forward, or creep, on a level
surface once the driver releases the brake with the engine
idling.
Moreover, starts upward on an incline are readily accommodated in a
gasoline vehicle because the creep of the automatic transmission
compensates for vehicle rollback during the time from when the
driver releases the brake until the driver can depress the
accelerator. In addition, even a conventional vehicle with a
standard transmission includes numerous contributors of rolling
friction which have a tendency to reduce the speed of rollback when
starting upward on an incline.
An electric vehicle may have one or more electric motors directly
driving the wheels as disclosed in U.S. Pat. No. 4,913,258 to
Sakuri et al. Alternately, an electric vehicle may have an electric
motor driving a set of wheels through a gearbox and differential.
Since the electric motor does not typically "idle" as a
conventional gasoline engine, a typical electric vehicle has a
tendency to first roll backwards when starting upward on an
incline. This rollback is particularly troublesome in traffic where
the vehicle may roll backwards into the vehicle behind. In
addition, when an electric vehicle rolls backward on a grade, the
motor is rotating in a direction opposite to the desired direction
of travel, and gear lash and drive shaft spring must first be taken
up from the drive train before the vehicle may begin to move
forward.
Current battery technology limits the driving range of an electric
vehicle to be considerably less than a gasoline vehicle.
Accordingly, much development has gone into reducing rolling
friction of the tires and various mechanical train drive components
of an electric vehicle to thereby improve efficiency and increase
the driving range. Unfortunately, the reduced rolling friction
exacerbates the problem of starting upward on an incline, since the
electric vehicle has a tendency to roll back even faster.
Battery powered vehicles, such as automobiles, forklifts, and other
utility vehicles, typically include some form of motor control
logic that may assist in starting the vehicle when the vehicle is
positioned on a grade. Creep, as in a gasoline vehicle, has been
simulated in an electric forklift for operation on a level surface
as shown in the graph of vehicle speed versus motor torque of FIG.
1, wherein a forward direction of intended movement is selected.
The forklift control computer applies power to the motor to
generate a predetermined constant output torque indicated by Point
A on the graph, irrespective of the vehicle speed.
It has also been common in electric vehicles to limit the rate at
which torque output can be increased from the electric motor to
provide for a smooth and jerk-free start. In other words, to
compensate for the lack of a clutch or fluid coupling, such as a
torque converter in a conventional gasoline-fueled vehicle, a timed
ramp on either the motor terminal voltage or armature current has
been used to regulate the rate of torque increase from the motor of
an electric vehicle.
Unfortunately, the timed ramp function is undesirable for starting
on a grade. For example, in order to limit the jerkiness when
starting on a level surface, the timed ramp is set to a relatively
slow initial setting so that torque does not build up too quickly;
however, with this same setting, substantial rollback may still
occur on a grade because of the slowness of increasing torque.
SUMMARY OF THE INVENTION
It is therefore object of the present invention to provide an
electric vehicle drive train and associated method for
counteracting rollback of the vehicle as when starting the vehicle
upward on a grade.
It is another object of the present invention to provide a drive
train and associated method for permitting smooth starting upward
on a grade.
These and other objects, features and advantages of the invention
are provided by an electric vehicle drive train including an
electric motor being rotatable in opposite directions corresponding
to respective opposite directions of actual vehicle movement,
sensing means associated with electric motor for sensing its
rotational direction, selector means for permitting driver
selection of a direction of intended vehicle movement, and rollback
detection and compensation means responsive to the sensing means
and the selector means for determining vehicle rollback and for
operating the electric motor to counteract the vehicle rollback.
Vehicle rollback is defined by a sensed direction of actual vehicle
movement opposite to a selected direction of intended vehicle
movement. The direction of actual vehicle movement corresponds to a
respective sensed rotational direction of the electric motor.
As would be readily understood by those skilled in the art, the
drive train preferably counteracts "backward" rollback when the
forward or "D" direction is selected and the vehicle is facing
upward on an incline. Similarly, the drive train counteracts
"forward" rollback when the "R" direction is selected and the
vehicle is facing backwards up an incline. As would also be readily
appreciated by those skilled in the art, the drive train may also
advantageously provide a smooth transition when the vehicle is
accidentally or inadvertently shifted into reverse, for example,
while moving in a forward direction. The present invention also
takes up gear lash and any spring in the drive shaft(s) to thereby
provide smoother starting.
The sensing means associated with the motor preferably includes
means for sensing a rotational speed of the motor which corresponds
to the speed of the vehicle, since the motor is typically coupled
to the vehicle wheels through a gear reduction transmission.
Accordingly, the rollback detection and compensation means includes
means for controlling the output torque magnitude of the electric
motor as a nonconstant function of rotational speed of the motor
during vehicle rollback. In one embodiment, the output torque
magnitude is controlled as a linear function of rotational speed of
the electric motor. In another embodiment, the output torque
magnitude is controlled as a function of the square of the sensed
rotational speed of the motor. Other nonconstant functions of
torque control based upon speed are also contemplated by the
present invention. The output torque magnitude of the electric
motor is also preferably set at a predetermined constant value
responsive to a rotational speed of the electric motor being above
a predetermined value.
The electric motor is preferably an induction motor utilizing a
form of vector control, such as achieved using a universal field
orientation controller, while those skilled in the art will
recognize that other types of electric motor drives having a
controllable output torque magnitude may also be used. The drive
train according to the invention also preferably includes a
traction battery carried by the vehicle frame. The traction battery
is also connected to the induction motor, such as through a
suitable power control circuit including a DC-to-AC inverter.
The drive train preferably also includes driver input means for
permitting driver selection of one of vehicle braking or vehicle
acceleration. The driver input means also preferably includes
conventional brake and accelerator pedals. Control means is
preferably connected to the electric motor for controlling the
output torque magnitude and rotational direction thereof in
response to the accelerator and brake pedals during normal driving
of the vehicle. The rollback detection and compensation means
cooperates with the control means to counteract vehicle rollback
even in an absence of driver selection of one of vehicle braking or
acceleration, as when the driver is moving his foot from the brake
pedal to the accelerator pedal. In other words, the drive train of
the present invention will closely mimic the operation of a
conventional gasoline-fueled vehicle having an automatic
transmission, by preventing substantial rollback when starting
upward on a hill. Rollback in an electric vehicle may be even more
severe than may occur with a conventional vehicle, because rolling
resistance is minimized in an electric vehicle to provide greater
range for a given battery capacity.
Another aspect of the invention is that the rollback detection and
compensation means includes means for generating a first torque
request value as a function of rotational speed of the electric
motor during vehicle rollback. The control means further includes
means for generating a second torque request value responsive to
the driver's selection of acceleration, for example, as when
starting upward on an incline. Accordingly, the rollback detection
and compensation means includes means for adding the first and
second torque request values together to control the magnitude of
the torque output of the electric motor. Thus, smoother
acceleration from a rollback condition is also provided by the
invention.
A method according to the invention for operating an electric
vehicle includes the steps of sensing a rotational direction of the
electric motor corresponding to a respective direction of actual
vehicle movement, determining vehicle rollback defined by the
sensed direction of actual vehicle movement being opposite the
intended direction of vehicle movement, and operating the electric
motor to counteract the vehicle rollback. The method further
preferably includes the step of sensing the rotational speed of the
electric motor. Accordingly, the step of operating the electric
motor to counteract the vehicle rollback includes the step of
operating the electric motor at an output torque magnitude as a
nonconstant function of sensed rotational speed of the electric
motor. This function may be either linear, or based upon the square
of speed, or based upon another nonconstant function of speed.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a graph of a motor torque and speed illustrating a
constant torque independent of speed for providing creep in an
electric forklift as in the prior art.
FIG. 2 is a perspective schematic fragmentary view of an electric
vehicle according to the present invention.
FIG. 3 is a schematic block diagram of an electric vehicle drive
train according to the invention.
FIG. 4 is a graph of vehicle speed versus motor torque illustrating
a linear function of torque output versus speed according to one
embodiment of the present invention.
FIG. 5 is a graph of vehicle speed versus motor torque illustrating
torque output as a function of the speed squared according to
another embodiment of the present invention.
FIG. 6 is a flow chart block diagram illustrating operation of the
drive train for an electric vehicle according to the present
invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention will now be described more fully hereinafter
with reference to the accompanying drawings, in which a preferred
embodiment of the invention are shown. This invention may, however,
be embodied in many different forms and should not be construed as
limited to the embodiments set forth herein. Rather, applicant
provides these embodiments so that this disclosure will be thorough
and complete, and will fully convey the scope of the invention to
those skilled in the art. Like numbers refer to like elements
throughout.
Referring first to FIG. 2 the drive train and its associated
components are illustrated installed in an electric vehicle 10
according to the invention. The vehicle 10 includes a body 11 that
may be carried by a separate supporting frame, or the vehicle may
be of unibody construction thereby having a body with an integral
frame, as would be readily understood by those skilled in the art.
The vehicle's wheels 12 are rotatably mounted to the frame. As
would also be readily understood by those skilled in the art, in
addition to applicability to an all-electric vehicle 10 as
described herein, the drive train according to the present
invention may also have applicability to hybrid types of electric
vehicles which include an additional power source, such as an
internal combustion engine.
A traction battery 13 is carried by the frame of the vehicle 10 in
a lower medial and rearward portion to thus provide a lower center
of gravity and more even weight distribution between the front and
rear wheels. As would be readily appreciated by those skilled in
the art, the traction battery 13 preferably comprises a plurality
of rechargeable interconnected battery cells.
The vehicle 10 preferably includes a Vehicle Control Unit (VCU) 14
which, among other tasks, determines and sends a desired torque
request signal to a control computer for a DC-to-AC inverter, both
of which are enclosed within a protective housing 15 under the hood
of the vehicle. The desired torque request signal is processed by
the control computer for the DC-to-AC inverter to drive the
electric motor 16 to the desired torque output magnitude, and in
the desired rotational direction corresponding to the intended
direction of vehicle movement.
The electric motor 16 may preferably be an induction motor
utilizing some form of vector control. However, those skilled in
the art will recognize that other types of electric motor drives
having a readily controllable output torque magnitude may also be
used. The vehicle 10 may also preferably include other related
components, such as a twelve volt accessory battery 17 and an
electrically-powered air conditioning compressor 18.
Referring now additionally to FIGS. 3-5, the drive train 20
according to the present invention is further explained. The drive
train components are controlled by control means, such as including
the controller 21 as illustrated. The controller 21 preferably
includes one or more microprocessors operating under stored program
control. For example, the control means may be provided by the VCU
14 and/or the control computer associated with the DC-to-AC
inverter (FIG. 2).
As would be readily understood by those skilled in the art, the
controller 21 may receive inputs from an "ignition" switch 25, an
accelerator position transducer 26, a brake position transducer 27,
and a gear selector (PRND) 28 for operating the electric motor 16
for driving and braking the vehicle. The gear selector 28 provides
selector means for permitting a driver to select an intended or
desired direction of vehicle movement, that is, either "D" for
forward movement, and "R" for reverse movement.
The controller 21 delivers power from the traction battery 13 to
the electric motor 16 during normal driving. The electric motor 16
is rotatable in opposite directions which correspond to respective
opposite directions of vehicle movement. In addition, the
controller 21 may also operate the motor 16 in a regenerative
braking mode wherein the motor is operated as a generator to slow
the vehicle, while simultaneously recharging the traction battery
13.
The electric motor 16 is connected to drive one or more of the
vehicle wheels 12 directly or through a transmission 22 as shown in
the illustrated embodiment. A differential, not shown, may be used
to permit a single motor to drive a set of vehicle wheels. The
electric motor 16 includes an output shaft 16a coupled to an input
of the transmission 22. The transmission 22, in turn, includes an
output shaft 22a coupled to one or more of the vehicle wheels 12 as
shown in the illustrated embodiment. First and second sensors 23a,
23b are preferably associated with respective shafts of the
electric motor 16 and the transmission 22. The sensors 23a, 23b
preferably provide both the rotational speed and the direction of
rotation for the electric motor 16 and transmission 22,
respectively.
The controller 21 includes rollback detection and compensation
means responsive to the sensing means 23a and selector means 28 for
determining vehicle rollback and for operating the electric motor
16 to counteract the vehicle rollback. Vehicle rollback is defined
by a sensed direction of actual vehicle movement opposite to a
selected direction of intended vehicle movement. The sensed
direction of vehicle movement corresponds to a respective
rotational direction of the electric motor 16.
The rollback detection and compensation means counteracts vehicle
rollback particularly even in the absence of driver selection of
one of vehicle braking or acceleration. In other words, the drive
train 20 of the present invention will closely mimic the operation
of an automatic transmission in a conventional gasoline-fueled
vehicle, by preventing substantial rollback when starting upward on
a hill.
As would be readily understood by those skilled in the art, the
rollback detection and compensation means of the drive train 20
preferably counteracts "backward" rollback when the forward or "D"
position is selected and the vehicle is facing up an incline. To
more clearly convey the invention, the following description is
directed to the case of starting upward on an incline in the
forward direction. Those of skill in the art will readily
appreciate the similar case contemplated by the invention for
counteracting "forward" rollback when the "R" position is selected
and the vehicle is facing backwards up an incline.
As would also be readily understood by those skilled in the art, in
addition to assisting in starting upward on an incline, the
rollback detection and compensation means also advantageously
provides a smooth transition when the vehicle is accidentally
shifted into reverse, for example, while the vehicle is moving in a
forward direction. In addition, the rollback detection and
compensation means may also take up gear lash and any spring in the
drive shaft(s) to thereby provide smoother starting on a hill.
The rollback detection and compensation means includes means for
controlling an output torque magnitude of the electric motor 16 as
a nonconstant function of rotational speed of the motor during
vehicle rollback. In one embodiment, the output torque magnitude of
the electric motor is a linear function of the sensed rotational
speed of the electric motor as shown in the graph of FIG. 4. The
upper right hand quadrant of the graph indicates the case where
forward is selected as the intended direction of vehicle movement
and the vehicle is moving in the forward direction, such as during
normal driving. The lower right hand quadrant of the graph
represents a rollback condition wherein a "positive" torque is
being produced, while the vehicle moves in a backward unintended
direction.
Accordingly, a linear function of torque output versus speed
provides the electric motor output torque magnitude to counteract
the vehicle rollback. The linear function intersects the x-axis for
torque at Point B. As also shown in the graph, if the motor speed,
and corresponding vehicle speed, is greater than a predetermined
value (Point C) on the y-axis, the motor output torque is
maintained at a constant level indicated by Point D on the x-axis
until the vehicle slows and the torque then follows the linear
portion of the curve.
As an example of the linear function, for an electric vehicle
weighing about 3500 lbs and a motor-to-wheel ratio of 12:1, and a
wheel rolling radius of 1 ft, a torque magnitude of about 110 lb ft
is required to hold the vehicle on a 30% grade. The 30% grade is
the typical maximum grade specification for an automobile. For the
vehicle and grade given, if the vehicle is limited to a maximum
rollback speed of about 1.5 mph (a 100 RPM speed of the motor) the
vehicle will be moving backward at a speed of about 1.5 ft/sec.
Thus, a gain constant can be chosen to provide 100 lb ft and 100
RPM, or one lb ft per RPM. As would be readily understood by those
skilled in the art, various gain constants can be used to adjust
for a wide range of vehicles and other specific rollback
speeds.
In addition to the linear torque output function, a torque output
function versus a square of the speed may also be implemented if a
"stiffer" or quicker recovery from rollback is desired as shown in
the graph of FIG. 5. As illustrated in FIG. 5, this function would
also preferably include a constant torque above a predetermined
speed value as described above. The points indicated in prime
notation in FIG. 5 are similar to those of FIG. 4. Other functions
of output torque magnitude versus vehicle speed are also
contemplated by the invention.
Another aspect of the invention is that the rollback detection and
compensation means includes means for generating a first torque
request value as a function of rotational speed of the electric
motor during vehicle rollback. The control means, such as the VCU
14 (FIG. 2) also includes means for generating a second torque
request value responsive to the driver's selection of acceleration.
Accordingly, the rollback detection and compensation means
preferably includes means for adding the first and second torque
request values together to control the magnitude of the torque
output of the electric motor.
Referring now to the flowchart of FIG. 6, operation of the drive
train according to the invention is explained. It will be
understood that these operations are preferably preferred by a
stored program in the control means although they may be performed
using other elements as well. After the start Block 30, the motor
speed and rotation, the brake and accelerator pedal position, and
gear selector are all monitored (Block 32). At Block 34 a rollback
determination is made based upon a backward movement of the vehicle
while the "D" or forward direction is selected by the driver.
If vehicle rollback is indicated at Block 34, a torque request
output value is determined as a function of the rollback speed at
Block 36. As described in greater detail above, the torque output
function may be linear, or based upon the square of the speed, or
may be based upon some other nonconstant function of speed. The
accelerator is monitored, and if the accelerator is not depressed
(Block 40), the motor is driven at Block 44 by the torque request
output value alone. If the accelerator has been depressed by the
driver at Block 40, the torque request based upon rollback is added
to a torque request based upon the accelerator position to drive
the motor (Block 44), thereby providing a smooth start upward on an
incline. As would be readily understood by those skilled in the
art, similar function relationships may be readily applied for the
rollback case where "R" is selected and the vehicle is facing
backwards up an incline.
Many modifications and other embodiments of the invention will come
to the mind of one skilled in the art having the benefit of the
teachings presented in the foregoing descriptions and the
associated drawings. Therefore, it is to be understood that the
invention is not to be limited to the specific embodiments
disclosed, and that modifications and embodiments are intended to
be included within the scope of the appended claims.
* * * * *